Not sure what you mean by "the canned stuff". If you are talking about sweetened condensed milk, then read no further because I have disobeyed your instructions!
I take a can of sweetened condensed milk. Put it unopened in a large pot of simmering water and leave for a couple of hours. That is certainly the easy way!

ChrisBird is spot on - this is how dulce de leche is made. The sweetened condensed milk slowly caramelizes and thickens.

I'll just add: make sure to keep the water topped up and always above the can(s) by several inches - or you could have an explosion on your hands. On the list of Things I Never Want to Clean, "dulce de leche from the underside of my rangehood" is surely up there.

Voted the Best Answer!

If you're worried about the can exploding (which is actually an issue, especially if you wander away and the water boils off and suddenly there's a very loud explosion in your kitchen and ants on your ceiling for months even though you've cleaned it a dozen times) is to bake it.
You pour two cans into a glass baking dish, place that into a roasting pan of water and bake without stirring at 350 until it's a nice rich caramel colour (check on it regularly), then you pour it into a bowl and whisk it until it's smooth (or smooth-ish at least, it sometimes has little tiny lumps, but they're delicious).

Yes, the above is wonderful and delicious, but dulce de leche can be made without a can. There are several methods, all involve cooking down milk, sugar and vanilla (start with good cream if you want a valid shortcut). Some recipes add baking powder, others add corn syrup, it all depends on how much time you have. Starting from scratch requires that you are in the kitchen stirring and watching for several hours. Is it worth the effort? Sometimes yes, sometimes no--all of the above work, but if you are starting with canned condensed milk is it really worthwhile compared to some of the excellent jarred varieties? Maybe. Personally, if I'm going to go to the trouble of fearing for bursting tins, I'm going for the real deal and cooking down rich cream with vanilla and sugar until it is the color of deep maple. True dulce de leche is spectacular.

I learned how to make DDL from scratch while living with a family in Ecuador. They use panela, an unrefined cane sugar with a mahogany brown color and a rich molasses flavor. I can't find that here, so I substitute turbinado sugar (Sugar in the Raw) which gives it that deep, rich caramel flavor and color. In my opinion, making DDL with very fresh whole milk is superior to using sweetened condensed milk (which I love to do on camping trips by sticking the can in the fire).

It does take a few hours to make, but the good news is that you can partially cook the DDL, hold it in the refrigerator, and then finish cooking later when you are back at the stove (or have friends to help stir).

Here's my recipe: Place 1 liter whole milk and 2 cups turbinado sugar into a 3-5 quart saucepan, and heat over medium low until just below a simmer, stirring to dissolve. Add 1/2 tsp. baking soda and stir (it will foam up). Keep at barely a simmer, stirring every 5-10 min. for the next 11/2 - 3 hours. Discard any milk scum that floats to the top. Be especially vigilant when the mixture starts to brown, stirring more frequently. The DDL is done when it is a deep caramel color and coats the back of a spoon. If not perfectly smooth, strain through a fine mesh sieve.